IL-18 is a pro-inflammatory cytokine, which belongs to the IL-1 cytokine family, is synthesized as a 24 kD precursor requiring caspase-1 for cleavage into an active 18 kD molecule, and has potent biological activities. For example, it induces interferon-γ (IFN-γ) production by T-cells and splenocytes, and was initially referred to as interferon-γ-inducing factor (IGIF) (Okamura et al., Nature 378(6552): 88-91 (1995); and Ushio et al., J. Immunol. 156: 4274-4279 (1996)). It also enhances the killing activity of natural killer (NK) cells, promotes the differentiation of naïve CD4+ T-cells into Th1 cells, augments the production of granulocyte-macrophage colony-stimulating factor (GM-CSF), and decreases the production of interleukin-10 (IL-10). Thus, IL-18 plays a key role in many inflammatory diseases, including allergy and autoimmune diseases.
A mouse protein, which induces IFN-γ by immunocompetent cells, was disclosed by Kabushiki Kaisha Hayashibara Seibutsu Kayaku Kenkyujo (“Hayashibara”; Okayama-shi, Japan) in European Pat. App. No. 0692536 (the '536 EP application), which was published on Jan. 17, 1996. Certain physicochemical properties and a defined partial amino acid sequence were also disclosed in the '536 EP application, as were a protein having 157 amino acids (aa), two fragments thereof, DNA (471 base pairs (bp)) encoding the protein, hybridomas, protein purification methods, and methods for detecting the protein.
A human protein having 157 aa, as well as homologues thereof, and DNA encoding the protein were disclosed by Hayashibara in European Pat. App. No. 0712931 (the '931 EP application), which was published on May 22, 1996. Transformants, processes for preparing the protein, monoclonal antibodies against the protein, hybridomas, protein purification methods, and methods for detecting the protein were also disclosed.
A human protein, which has a specific 10-aa sequence near its N-terminus and which induces IFN-γ production by an immunocompetent cell, was disclosed by Hayashibara in European Pat. App. No. 0767178 (the '178 EP application), which was published on Apr. 9, 1997. Also disclosed were processes for producing the protein, and characterizations of the protein as a pharmaceutical agent, in particular an anti-oncotic or anti-tumor agent, an antiviral agent, an antibacterial agent, and an agent for the treatment of immunopathy and atopic diseases.
A precursor to IL-18 having 193 aa was disclosed by Incyte Pharmaceuticals, Inc., in Int'l Pat. App. No. WO 97/24441, which was published on Jul. 10, 1997. Also disclosed was the DNA encoding the precursor.
In addition to its potent biological activities, IL-18 has been determined to be a renal marker for various conditions or disease states, including, but not limited to, inflammatory disorders, e.g., allergy and autoimmune disease (Kawashima et al., J. Educ. Inform. Rheumatology 26 (2): 77 (1997)), acute kidney injury (Parikh et al., J. Am. Soc. Nephrol. 16: 3046-3052 (2005); and Parikh et al., Kidney Int'l 70: 199-203 (2006)), chronic kidney disease (such as when used as part of a panel assay), and minimal-change nephritic syndrome (MCNS) (Matsumoto et al., Nephron 88: 334-339 (2001)). Unfortunately, IL-18 is highly unstable at 37° C., and even at 22° C. (i.e., room temperature), especially in the absence of protein. This instability makes assaying for the presence or the level of IL-18 in a biological sample, such as urine, difficult due to the rapid loss of activity of IL-18 in control or calibrator compositions. Yamamoto et al. (Biochem. Biophys. Res. Comm. 317: 181-186 (2004)) has proposed replacing cysteine residues with serine in an effort to stabilize IL-18.
It is an object of the present disclosure to provide a more stable IL-18, which does not involve amino acid replacement. It is another object of the present disclosure to provide compositions comprising such an IL-18, as well as kits, and methods of making and using the IL-18. These and other objects, as well as inventive features, will become apparent from the detailed description provided herein.